Communication system, communication device, and data frame retransmission control method

ABSTRACT

A mobile station device ( 12 ) includes a retransmission request transmission timing identifying unit ( 40 ) which identifies, based on a timing of reception of a data frame transmitted from a base station device, a timing of transmission of a retransmission request of the data frame to the base station device. The base station device includes a retransmission data frame selecting unit which selects, based on a timing of reception of the retransmission request transmitted from the mobile station device ( 12 ), a data frame to be retransmitted from among a plurality of data frames transmitted to the mobile station device ( 12 ), and retransmits a data frame selected by the retransmission data frame selecting unit to the mobile station device ( 12 ).

TECHNICAL FIELD

The present invention relates to a communication system, a communicationdevice, and a data frame retransmission control method.

BACKGROUND ART

In an ARQ (Automatic Repeat Request) method which is one of errorcorrection methods, when there is an error in a received data frame, thereceiving side transmits a retransmission request of the data frame tothe transmitting side. The transmitting side identifies the data frameto be retransmitted based on the received retransmission request, andretransmits the data frame to the receiving side. The retransmissionrequest includes a sequence number (order number) for identifying thedata frame to be retransmitted, and the transmitting side identifies therequested data frame based on the sequence number and retransmits therequested data frame (for example, refer to Patent Document 1).

For improving the error correction efficiency in the ARQ method, it iseffective to reduce the number of retransmissions of the data frame,reduce the time period from reception of the retransmission request toretransmission of the data frame, etc. In this regard, Patent Document 2discloses a wireless transmitting device to which a hybrid ARQ isapplied wherein the number of retransmissions of the data frame isreduced so that the system throughput is improved.

[Patent Document 1] JP 10-117182 A [Patent Document 2] JP 2004-253828 ADISCLOSURE OF THE INVENTION

However, in the ARQ method of the related art as described above, thedata size of the retransmission request is enlarged corresponding to thenumber of bits of the sequence number. In particular, when communicationdata and other data are transmitted along with the retransmissionrequest, it is desired that the number of bits assigned to theretransmission request be reduced so that more number of bits can beassigned to the communication data or the like.

In addition, because a certain processing time (hereinafter referred toas “reference required time”) is required from the reception of theretransmission request to the retransmission of the data frame, it maybecome difficult to retransmit the data frame using the transmissionframe immediately following the frame in which the retransmissionrequest is received, particularly in a communication according to aTDMA/TDD (Time Division Multiple Access/Time Division Duplex) system.Because of this, in the ARQ of the related art applied to the TDMA/TDDsystem, in order to secure a sufficient time for the retransmissionprocess of the data frame, the data frame is uniformly retransmittedusing the transmission frame of two or more frames later than the framein which the retransmission request is received. As a result, there is aproblem in that a retransmission delay of greater than or equal to 1TDMA frame always occurs when there is an error in the data frame.

The present invention was conceived in view of the above-describedproblem of the related art, and a first object is to provide acommunication system, a receiving device, a transmitting device, and adata frame retransmission control method which can achieve an automaticretransmission control of the data frame without including the sequencenumber of the data frame in the retransmission request.

A second object is to provide a communication device and a data frameretransmission method which can preferably shorten the time from thereception of the retransmission request to the retransmission of thedata frame.

In order to achieve the first object, a communication system accordingto the present invention is a communication system having a transmittingdevice and a receiving device which employ an automatic repeat requestmethod of a data frame, wherein the receiving device includesretransmission request transmission timing identifying means foridentifying, based on a timing of reception of a data frame transmittedfrom the transmitting device, a timing of transmission of aretransmission request of the data frame to the transmitting device, thetransmitting device includes retransmission data frame selecting meansfor selecting, based on a timing of reception of the retransmissionrequest transmitted from the receiving device, a data frame to beretransmitted from among a plurality of data frames transmitted to thereceiving device, and retransmits the data frame selected by theretransmission data frame selecting means to the receiving device.

According to the present invention, the receiving device identifies,based on a reception timing of a data frame (transmission timing for thetransmitting device), a response timing (reception timing for thetransmitting device) of the retransmission request for the data frame.On the other hand, the transmitting device identifies, based on thereception timing of the retransmission request, the timing when the dataframe corresponding to the retransmission request was transmitted. Inother words, in this communication system, the receiving device and thetransmitting device share the timing difference (time interval) betweenthe transmission (reception) timing of the data frame and the reception(transmission) timing of the retransmission request for the data frame.Because of this configuration, even if the sequence number of the dataframe is omitted in the retransmission request, the transmitting devicecan identify to which data frame the received retransmission requestcorresponds.

The transmitting device may further include transmitted data framestorage means for storing at least some of the plurality of data framestransmitted to the receiving device in a manner to allow identificationof a timing of transmission of each of the data frames, and theretransmission data frame selecting means may identify a timing oftransmission of the data frame to be retransmitted based on the timingof reception of the retransmission request and select the data frame tobe retransmitted from the transmitted data frame storage means based onthe identified timing.

The communication system may further employ a time division multiplexcommunication system, and the timing may be identified by a time slot ora time frame according to time division multiplexing.

A receiving device according to the present invention is a receivingdevice which receives a data frame transmitted from a transmittingdevice and which transmits, upon detection of an error in the receiveddata frame, a retransmission request of the data frame to thetransmitting device, the receiving device including retransmissionrequest transmission timing identifying means for identifying, based ona timing of reception of the data frame, a timing of transmission of theretransmission request of the data frame.

A transmitting device according to the present invention is atransmitting device which transmits a data frame to a receiving deviceand which retransmits, in response to a retransmission request from thereceiving device, a data frame corresponding to the retransmissionrequest, the transmitting device including retransmission data frameselecting means for selecting, based on a timing of reception of theretransmission request, a data frame to be retransmitted from among aplurality of data frames transmitted to the receiving device, andretransmits a data frame selected by the retransmission data frameselecting means to the receiving device.

A data frame retransmission control method according to the presentinvention is a data frame retransmission control method in acommunication system having a transmitting device and a receivingdevice, the data frame retransmission control method including aretransmission request transmission timing identifying step ofidentifying, based on a timing at which the receiving device receives adata frame transmitted from the transmitting device, a timing oftransmission of a retransmission request of the data frame to thetransmitting device, and a retransmission data frame selecting step ofselecting, based on a timing at which the transmitting device receivesthe retransmission request, a data frame to be retransmitted from amonga plurality of data frames transmitted to the receiving device.

In order to achieve the second object, a communication device accordingto the present invention is a communication device which communicateswith another communication device according to a time division duplexsystem and which retransmits, in response to a retransmission requesttransmitted from the other communication device, a data framecorresponding to the retransmission request to the other communicationdevice, the communication device including data frame retransmissiontiming determining means for determining a retransmission timing of thedata frame based on a reception timing of the retransmission request sothat a timing difference between the reception timing of theretransmission request and the retransmission timing of the data framecorresponding to the retransmission request is close to a referencerequired time required from reception of a retransmission request toretransmission of a data frame.

According to the present invention, a retransmission timing of a dataframe is determined based on a reception timing of the retransmissionrequest so that the time from reception of the retransmission request tothe retransmission of the data frame is close to a reference requiredtime required for the retransmission process of the data frame. Becauseof this configuration, it is possible to preferably shorten the timefrom the reception of the retransmission request to the retransmissionof the data frame.

The communication device may further include timing differenceinformation storage means for storing, in correlation to informationindicating a reception timing of a retransmission request, timingdifference information indicating a timing difference which satisfies acondition related to the reference required time, wherein the data frameretransmission timing determining means may read timing differenceinformation from the timing difference information storage means incorrelation to the reception timing of the retransmission request anddetermine the retransmission timing of the data frame based on thereception timing of the retransmission request and the read timingdifference information.

A communication device according to the present invention is acommunication device which communicates with another communicationdevice according to a time division duplex system and which retransmits,in response to a retransmission request transmitted from the othercommunication device, a data frame corresponding to the retransmissionrequest to the other communication device, the communication deviceincluding data frame retransmission timing determining means fordetermining a retransmission timing of the data frame based on aprocessing capability of the communication device so that a timingdifference between a reception timing of the retransmission request andthe retransmission timing of the data frame corresponding to theretransmission request is close to a reference required time requiredfrom reception of a retransmission request to retransmission of a dataframe.

According to the present invention, the retransmission timing of thedata frame is determined in consideration of the processing capabilityof the communication device so that the time from reception of theretransmission request to the retransmission of the data frame is closeto the reference required time required for retransmission process ofthe data frame. Because of this configuration, it is possible topreferably shorten the time from the reception of the retransmissionrequest to the retransmission of the data frame.

The data frame retransmission timing determining means may determine theretransmission timing of the data frame further based on the receptiontiming of the retransmission request. With such a configuration, it ispossible to determine the retransmission timing of the data framefurther based on, in addition to the processing capability of thecommunication device, the reception timing of the retransmissionrequest. Thus, it is possible to more preferably shorten the time fromthe reception of the retransmission request to the retransmission of thedata frame.

The communication device may further include timing differenceinformation storage means for storing, in correlation to informationindicating a processing capability of a communication device andinformation indicating a reception timing of a retransmission request,timing difference information indicating a timing difference whichsatisfies a condition related to the reference required time, whereinthe data frame retransmission timing determining means may read thetiming difference information from the timing difference informationstorage means in correlation to the processing capability of thecommunication device and the reception timing of the retransmissionrequest and determine the retransmission timing based on the receptiontiming of the retransmission request and the read timing differenceinformation.

The reception timing may be identified by a reception slot, and theretransmission timing may be identified by a transmission slot or atransmission frame including the transmission slot.

A data frame retransmission method according to the present invention isa data frame retransmission method in which a data frame isretransmitted in response to a retransmission request in a communicationaccording to a time division duplex system, the data frameretransmission method including a step of determining a retransmissiontiming of the data frame based on a reception timing of theretransmission request so that a timing difference between the receptiontiming of the retransmission request and the retransmission timing ofthe data frame corresponding to the retransmission request is close to areference required time required from reception of a retransmissionrequest to retransmission of a data frame.

A data frame retransmission method according to the present invention isa data frame retransmission method in which a data frame isretransmitted in response to a retransmission request in a communicationaccording to a time division duplex system, the data frameretransmission method including a step of determining a retransmissiontiming of the data frame based on a processing capability of thecommunication device so that a timing difference between a receptiontiming of the retransmission request and the retransmission timing ofthe data frame corresponding to the retransmission request is close to areference required time required from reception of a retransmissionrequest to retransmission of a data frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall configuration diagram of a mobile communicationsystem according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of a mobile station deviceaccording to the first embodiment of the present invention.

FIG. 3 is a functional block diagram of a base station device accordingto the first embodiment of the present invention.

FIG. 4 is a diagram showing an example of a time slot structureaccording to TDMA/TDD and a subchannel structure according to OFDMA.

FIG. 5 is a diagram showing an example of a PHY frame structure in anuplink.

FIG. 6 is a diagram for explaining a transmission timing of aretransmission request.

FIG. 7 is a flowchart showing a data frame transmission (andretransmission) process in the base station device.

FIG. 8 is a flowchart showing an error correction process of a receiveddata frame in the mobile station device.

FIG. 9 is an overall configuration diagram of a mobile communicationsystem according to a second embodiment of the present invention.

FIG. 10 is a functional block diagram of a mobile station deviceaccording to the second embodiment of the present invention.

FIG. 11 is a diagram showing an example of a timing differenceinformation storage unit.

FIG. 12 is a diagram showing an example of a time slot structureaccording to TDMA/TDD and a subchannel structure according to OFDMA.

FIG. 13 is a diagram for explaining a retransmission timing of a dataframe.

FIG. 14 is a flowchart showing a process for acquiring timing differenceinformation in the mobile station device.

FIG. 15 is a flowchart showing a data frame transmission (andretransmission) process in the mobile station device.

FIG. 16 is an overall configuration diagram of a mobile communicationsystem according to a third embodiment of the present invention.

FIG. 17 is a functional block diagram of a mobile station deviceaccording to the third embodiment of the present invention.

FIG. 18 is a diagram showing an example of a timing differenceinformation storage unit.

FIG. 19 is a diagram showing an example of a time slot structureaccording to TDMA/TDD and a subchannel structure according to OFDMA.

FIG. 20 is a diagram for explaining a retransmission timing of a dataframe.

FIG. 21 is a flowchart showing a process for acquiring timing differenceinformation in the mobile station device.

FIG. 22 is a flowchart showing a data frame transmission (andretransmission) process in the mobile station device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings.

First Embodiment

FIG. 1 is an overall configuration diagram of a mobile communicationsystem according to a first embodiment of the present invention. Asshown in FIG. 1, the mobile communication system 1 includes a basestation device 10 and a plurality of mobile station devices 12 (here,three mobile station devices).

Each of the mobile station devices 12 wirelessly communicates with thebase station device 10, and may be, for example, a portable cellularphone, a personal digital assistant, or a communication card. In thisconfiguration, the mobile station device 12 transmits and receives datato and from the base station device 10 according to a TDD (Time DivisionDuplex) system and executes a multiplex communication according to aTDMA (Time Division Multiple Access) system and an OFDMA (OrthogonalFrequency Division Multiple Access) system. In addition, the basestation device 10 includes an adaptive array antenna as will bedescribed below, and executes a multiplex communication with each of theplurality of mobile station devices 12 at a same time slot and a samecarrier frequency according to an SDMA (Space Division Multiple Access)system using the adaptive array antenna. In this manner, a bidirectionalcommunication with the plurality of mobile station devices 12 isexecuted with a very high frequency usage efficiency.

FIG. 4 is a diagram showing an example of a time slot structure (1 TDMAframe) according to TDMA/TDD and a subchannel structure according toOFDMA. As shown in FIG. 4, each of a downlink (wireless transmissionpath from the base station device 10 to the mobile station device 12)and an uplink (wireless transmission path from the mobile station device12 to the base station device 10) includes 4 time slots. Each time slotincludes 28 subchannels, one of which is used as a control channel (CCH)and the remaining 27 of which are used as traffic channels (TCH).

The base station device 10 assigns at least some of a total of 108subchannels (27 subchannels×4 slots) used as the traffic channels toeach of the mobile station devices 12 in each of the downlink and theuplink. More specifically, as shown in FIG. 4, the base station device10 assigns one anchor subchannel (ASCH) and assigns one or a pluralityof extra subchannels (ESCH) as necessary, for each mobile station device12.

The ASCH is a subchannel which is determined when a link is established(at the start of communication) and notified to each of the mobilestation devices 12 using the CCH, and is used for transmitting andreceiving MAP information and other control information. The MAPinformation is a bit sequence having a length of 108 bits indicating oneor a plurality of ESCH to be used in the next TDMA frame (next uplinkframe and downlink frame) after the MAP information is received. Morespecifically, a bit corresponding to ESCH to be assigned to the mobilestation device 12 in the next TDMA frame is indicated with “1” and bitscorresponding to the other subchannels (ASCH, ESCH to be assigned toother mobile station devices 12, and idle subchannel) are indicated with“0”. The ESCH, on the other hand, is a subchannel which is determinedafter the link is established and is identified by the MAP informationnotified to the mobile station device 12 using the ASCH, and isprimarily used for transmission and reception of communication data. Asshown in FIG. 4, the ASCH and ESCH are assigned to the same subchannelin the downlink slot and the uplink slot having corresponding slotnumbers (DL#1 and UL#1, DL#2 and UL#2, . . . ).

FIG. 5 is a diagram showing an example of a PHY (Physical Layer) framestructure in the uplink. Data of 1 PHY frame is transmitted in 1 TDMAframe. More specifically, the data of 1 PHY frame is distributed overSCH (Subchannel) payloads corresponding to one ASCH and one or aplurality of ESCH in each TDMA frame and is transmitted. As shown inFIG. 5, the PHY frame includes a PHY header including ACKCH, RMAP, etc.,and a plurality of PHY data units including PHY payload, etc. In thepresent embodiment, a data frame to be retransmitted indicates the PHYframe, and the retransmission of the PHY frame is controlled using ahybrid ARQ method.

In this configuration, the ACKCH (Acknowledge Channel) is a region whichstores ACK (Acknowledge) or NACK (Negative Acknowledge) indicatingpresence or absence of error in the data frame received in downlink. Inparticular, when the ACKCH stores NACK, the ACKCH represents aretransmission request of a data frame. A characteristic of the presentembodiment is that ARQ is achieved without including the sequence numberof the data frame in the retransmission request and that, as a result,the PHY header size can be reduced.

The RMAP (Refuse MAP) is a region which stores RMAP information having asame size as the MAP information. The RMAP information is a bit sequencehaving a length of 108 bits indicating the ESCH refusing the assignmentfrom the base station device 10 in the next TDMA frame. Morespecifically, the RMAP information is a bit sequence having a length of108 bits indicating the ESCH refusing the assignment from the basestation device 10 in the next TDMA frame, and indicates a bitcorresponding to the ESCH refusing the assignment with “1” and the otherbits with “0”.

Configurations and operations of the base station device 10 and themobile station device 12 will now be described.

FIG. 2 is a functional block diagram of the mobile station device 12. Asshown in FIG. 2, the mobile station device 12 includes an antenna 20, awireless communication unit 22, a signal processor 24, amodulation/demodulation unit 26, a maximum ratio combining unit 28, areceive buffer 30, an error correcting unit 32, an error detecting unit34, and a retransmission request transmission controller 36.

The wireless communication unit 22 includes a low noise amplifier, adown-converter, and an up-converter. The wireless communication unit 22down-converts a wireless signal from the base station device 10 receivedby the antenna 20 and outputs to the signal processor 24. The wirelesscommunication unit 22 also up-converts a transmission signal which isinput from the signal processor 24 into a wireless signal, amplifies thewireless signal to a transmission power level, and transmits from theantenna 20.

The signal processor 24 executes processes such as symbolsynchronization and removal of a guard interval (GI) signal on thesignal which is input from the wireless communication unit 22, toacquire a baseband OFDM signal, and outputs to themodulation/demodulation unit 26. The signal processor 24 also adds aguard interval signal to a baseband OFDM signal which is input from themodulation/demodulation unit 26 and outputs to the wirelesscommunication unit 22.

The modulation/demodulation unit 26 includes an A/D converter, an FFTunit, and a channel estimation unit. The modulation/demodulation unit 26OFDM-demodulates the baseband OFDM signal which is input from the signalprocessor 24 and outputs the acquired received data frame (datacorresponding to 1 downlink frame) to the maximum ratio combining unit28. More specifically, after the modulation/demodulation unit 26A/D-converts the baseband OFDM signal, the modulation/demodulation unit26 applies an FFT in the FFT unit, to acquire subcarrier components ofthe OFDM symbol. After the modulation/demodulation unit 26 applies apredetermined channel estimation process or the like, themodulation/demodulation unit 26 connects the subcarrier componentscorresponding to a plurality of subchannels (one ASCH and one or aplurality of ESCH) assigned by the base station device 10, to create asymbol sequence. The modulation/demodulation unit 26 then outputs thesymbol sequence to the maximum ratio combining unit 28.

The modulation/demodulation unit 26 also includes a symbol mapping unit,an IFFT unit, and a D/A converter. The modulation/demodulation unit 26OFDM-modulates a transmission data which is input from an externalconnection device or data input unit (not shown) and outputs theacquired baseband OFDM signal to the signal processor 24. Morespecifically, the modulation/demodulation unit 26 distributes thetransmission data over a plurality of PHY payloads, and adds a PHYheader including ACKCH which stores ACK or NACK which is input from theretransmission request transmission controller 36 to a PHY data unitacquired by combining the PHY payloads, to construct a predetermined PHYframe. Then, the modulation/demodulation unit 26 divides the datacorresponding to the PHY frame to SCH payloads corresponding to aplurality of subchannels (one ASCH and one or a plurality of ESCH)assigned by the base station device 10, to create transmission data foreach subchannel. During this process, the data sequence including theACKCH is assigned to the SCH payload corresponding to the ASCH. Then,the modulation/demodulation unit 26 converts the created transmissiondata of each of the subchannels into a symbol sequence through a symbolmapping and distributes the symbol sequence over subcarriers of thesubchannel. The modulation/demodulation unit 26 then applies an IFFT inthe IFFT unit and outputs the baseband OFDM signal acquired through aD/A conversion to the signal processor 24.

The maximum ratio combining unit 28 maximum-ratio combines a symbolsequence created from the received data frame which is input from themodulation/demodulation unit 26 and a symbol sequence created from pastreceived data frame which is input from the receive buffer 30, and isprovided for improving an error correction percentage of the receiveddata in the error correcting unit 32. The symbol sequence created fromthe past received data frame is read from the receive buffer 30 based onthe sequence number of the received data frame which is input from themodulation/demodulation unit 26.

The receive buffer 30 stores a symbol sequence which is input from themaximum ratio combining unit 28 in correlation to the sequence number ofthe received data frame. The symbol sequence for which no error isdetected by the error detecting unit 34 is deleted from the receivebuffer 30 at a predetermined timing.

The error correcting unit 32 applies an extraction of a bit sequence andan error correction with a predetermined error correction algorithm, onthe symbol sequence which is input from the maximum ratio combining unit28. If an error is not corrected in the error correcting unit 32, theerror is detected by the error detecting unit 34 which is at downstreamof the error correcting unit 32.

The error detecting unit 34 detects whether or not there is a data errorin the data after error correction which is input from the errorcorrecting unit 32. The error detecting unit 34 outputs, as the receiveddata, only the data for which no error is detected to the externalconnection device (not shown). The data for which an error is detectedis set as a target of the retransmission request, and the data is notoutput to the external connection device until the correct data frame isretransmitted from the base station device 10. A detection result by theerror detecting unit 34 is output to the retransmission requesttransmission controller 36. As the method of detecting error, forexample, CRC (Cyclic Redundancy Check) is employed.

The retransmission request transmission controller 36 includes a dataframe reception timing acquiring unit 38, a retransmission requesttransmission timing identifying unit 40, and a timing differenceinformation storage unit 42, and creates ACK or NACK based on the errordetection result which is input from the error detecting unit 34. Theretransmission request transmission controller 36 applies a control totransmit the created ACK or NACK to the base station device 10 at apredetermined timing without adding the sequence number of the dataframe. More specifically, the retransmission request transmissioncontroller 36 creates ACK when no error is detected in the errordetecting unit 34 and creates NACK when an error is detected. Theretransmission request transmission controller 36 outputs the createdACK or NACK to the modulation/demodulation unit 26 so that the createdACK or NACK is transmitted at a timing identified by the retransmissionrequest transmission timing identifying unit 40 to be described later.

The data frame reception timing acquiring unit 38 acquires a receptiontiming of each received data frame acquired by themodulation/demodulation unit 26. The reception timing may be identifiedby the downlink slot or the downlink frame when the data frame isreceived, and information on which of the downlink slot or the downlinkframe is to be used as the reception timing is shared between eachmobile station device 12 and the base station device 10 in advance.

The timing difference information storage unit 42 stores timingdifference information indicating a timing difference (time interval)between the reception timing of the data frame and the transmissiontiming of the retransmission request for the data frame. The timingdifference information may be time or may be the number of TDMA slots orthe number of TDMA frames, and is same information as timing differenceinformation stored in a timing difference information storage unit 66 ofthe base station device 10. In other words, the timing differencebetween the reception (transmission) timing of the data frame and thetransmission (reception) timing of the retransmission request for thedata frame is shared between each mobile station device 12 and the basestation device 10 in advance. The timing difference information may bedefined in the mobile communication system 1 in advance or may bedetermined between each mobile station device 12 and the base stationdevice 10 at the start of the communication.

The retransmission request transmission timing identifying unit 40identifies a timing of transmission of the retransmission request of thedata frame based on the timing of reception of the data frame which istransmitted from the base station device 10. More specifically, theretransmission request transmission timing identifying unit 40identifies the transmission timing of the ACK or the NACK for the dataframe based on the reception timing of the data frame acquired by thedata frame reception timing acquiring unit 38 and the timing differenceinformation (information indicating a timing difference betweenreception timing of the data frame and the transmission timing of theretransmission request for the data frame) stored in the timingdifference information storage unit 42. The transmission timing may beidentified by the uplink slot or the uplink frame in which the ACK orthe NACK is transmitted, and information on which of the uplink slot andthe uplink frame is used as the transmission timing is shared betweeneach mobile station device 12 and the base station device 10 in advance.

FIG. 6 is a diagram for explaining a transmission timing of theretransmission request identified by the retransmission requesttransmission timing identifying unit 40. Here, a case will be describedin which the timing difference information stored in the timingdifference information storage unit 42 is “1 TDMA frame (frame afternext frame)” and the ASCH for transmitting data including ACKCH is thefirst slot. As shown in FIG. 6, when the data frame reception timingacquiring unit 38 acquires the downlink frame in which the data framefor which an error is detected is received, the retransmission requesttransmission timing identifying unit 40 identifies the uplink slot(here, the first slot) of the “frame after the next frame” of thedownlink frame as the transmission timing of the retransmission request(NACK) for the data frame.

Next, FIG. 3 is a block diagram of the base station device 10. As shownin FIG. 3, the base station device 10 includes an adaptive array antenna50, a wireless communication unit 52, a signal processor 54, amodulation/demodulation unit 56, a data buffer 58, and a data frameretransmission controller 62.

The adaptive array antenna 50 is an array of a plurality of antennas.The adaptive array antenna 50 receives a wireless signal transmittedfrom the mobile station devices 12 at the antennas and outputs thereceived signal to the reception unit 22. The adaptive array antenna 50also transmits a signal which is input from the wireless communicationunit 52 through the antennas. The reception and transmission areswitched in a time divisional manner.

The wireless communication unit 52 includes a low noise amplifier, adown-converter, and an up-converter. The wireless communication unit 52down-converts the wireless signal received by the adaptive array antenna50 and outputs to the signal processor 24. The wireless communicationunit 52 also up-converts the transmission signal which is input from thesignal processor 24 into a wireless signal, amplifies the wirelesssignal to a transmission power level, and supplies to the adaptive arrayantenna 50.

The signal processor 54 includes a space division multiplex processorand a time division multiplex processor. The signal processor 54acquires a baseband OFDM signal from a signal which is input from thewireless communication unit 52 and outputs to themodulation/demodulation unit 56. In other words, because space divisionmultiple access (SDMA), time division multiple access (TDMA), andorthogonal frequency division multiple access (OFDMA) are applied to thesignal which is input from the wireless communication unit 52, thesignal processor 54 applies a space division process related to a weightcontrol of the adaptive array antenna 50 and time division process onthe signal. Then, the signal processor 54 executes processes such as asymbol synchronization and removal of guard interval signal on theseparated signal, and acquires the baseband OFDM signal. The basebandOFDM signal acquired in this manner is output to themodulation/demodulation unit 56.

The signal processor 54 also adds the guard interval signal to thebaseband OFDM signal which is input from the modulation/demodulationunit 56, creates a signal to which the time division multiplex processand the space division multiplex process related to the weight controlof the adaptive array antenna 50 are applied, and outputs to thewireless communication unit 52.

The modulation/demodulation unit 56 includes an A/D converter, an FFTunit, a channel estimation unit, and a de-mapping unit. Themodulation/demodulation unit 56 OFDM-demodulates the baseband OFDMsignal which is input from the signal processor 54 and outputs theacquired received data frame (data corresponding to 1 uplink frame) fromeach mobile station device 12 to the data buffer 58. Themodulation/demodulation unit 56 also includes a symbol mapping unit, anIFFT unit, and a D/A converter. The modulation/demodulation unit 56OFDM-modulates a transmission data frame (data corresponding to 1downlink frame) which is input from the data buffer 58 (a transmissionqueue 60), and outputs the acquired baseband OFDM signal to the signalprocessor 54. The contents of the process in the modulation/demodulationunit 56 are approximately common with the contents of the processes inthe modulation/demodulation unit 26 in the mobile station device 12,and, thus, will not be described here in detail.

The data buffer 58 includes the transmission queue 60. The data buffer58 temporarily stores the received data frames from the mobile stationdevices 12 which are input from the modulation/demodulation unit 56 andsequentially outputs received data which is acquired by connecting thereceived data frames to a predetermined upper device (not shown). Thedata buffer 58 also temporarily stores transmission data frames to eachof the mobile station devices 12 which are input from the upper deviceand the data frame retransmission controller 62 and sequentially outputsto the modulation/demodulation unit 56 through the transmission queue60.

The transmission queue 60 holds the transmission data frames in a liststructure of a First In First Out (FIFO) method. The transmission dataframe or the retransmission data frame which is input from the dataframe retransmission controller 62 is added to the transmission queue 60in each TDMA frame. In addition, the first data frame in thetransmission queue 60 is extracted in each TDMA frame and is output tothe modulation/demodulation unit 56.

The data frame retransmission controller 62 includes a retransmissionrequest acquiring unit 64, a timing difference information storage unit66, a transmission-complete queue (transmitted data frame storage unit)68, and a retransmission data frame selecting unit 70. The data frameretransmission controller 62 controls, in response to a retransmissionrequest transmitted from each mobile station device 12, retransmissionof the data frame corresponding to the retransmission request.

The retransmission request acquiring unit 64 acquires, in each TDMAframe, the ACKCH of the PHY header shown in FIG. 5 from the receiveddata which is output from the data buffer 58, and acquires a receptiontiming of the data frame including the ACKCH. The reception timing maybe identified by a downlink slot or a downlink frame in which theretransmission request is received, and information on which timing isused as the reception timing is shared between the base station device10 and each mobile station device 12 in advance.

The timing difference information storage unit 66 stores timingdifference information indicating a timing difference between thetransmission timing of the data frame and the reception timing of theretransmission request for the data frame. The timing differenceinformation may be time or the number of TDMA slots or the number ofTDMA frames, and is the same information as the timing differenceinformation stored in the timing difference information storage unit 42of the mobile station device 12. In other words, the timing differencebetween the transmission (reception) timing of the data frame and thereception (transmission) timing of the retransmission request for thedata frame is shared between the base station device 10 and each mobilestation device 12 in advance. Because of this configuration, the basestation device 10 can identify the timing of transmission of the dataframe corresponding to the ACK or the NACK based on the reception timingof the ACK or the NACK even though the sequence number of the receiveddata frame is not added to the ACK or the NACK transmitted from themobile station device 12. The timing difference information may bedefined in the mobile communication system 1 in advance or may bedetermined between the base station device 10 and each mobile stationdevice 12 at the start of the communication.

The transmission-complete queue 68 holds at least some of the pluralityof data frames transmitted to the mobile station devices 12 in a liststructure of a First In First Out (FIFO) method, and functions as atransmitted data frame storage unit. The first data frame in thetransmission queue 60 is transmitted in each TDMA frame, and with thetransmission, the data frame is extracted from the transmission queue 60and added to the transmission-complete queue 68. In thetransmission-complete queue 68, an upper limit is set in the number oftransmitted data frames to be held and the transmission-complete queue68 is configured to allow identification of the timing of transmissionof each of the data frames.

More specifically, the transmission-complete queue 68 has a sizecorresponding to the timing difference information (informationindicating a timing difference between the transmission timing of a dataframe and a reception timing of the retransmission request for the dataframe) stored in the timing difference information storage unit 66. Forexample, when the timing difference information is “1 TDMA frame”, thetransmission-complete queue 68 has a size to allow holding of 2 TDMAframes acquired by adding 1 TDMA frame to the timing differenceinformation, that is, the transmission-complete queue 68 has a size toallow holding of a maximum of two transmitted data frames. Similarly,when the timing difference information is 2 TDMA frames, thetransmission-complete queue 68 has a size to allow holding of a maximumof three transmitted data frames. With this configuration, the ACKCHacquired by the retransmission request acquiring unit 64 in each TDMAframe would correspond to the first data frame in thetransmission-complete queue 68 at the timing of reception of the ACKCH.

Because of this, when the NACK is stored in the ACKCH acquired by theretransmission request acquiring unit 64, the first data frame isextracted from the transmission-complete queue 68 as the retransmissiondata frame and is added to the transmission queue 60. When, on the otherhand, the ACK is stored in the ACKCH, the first data frame does not needto be retransmitted and is deleted.

In this configuration, the transmission-complete queue 68 is used as thetransmitted data frame storage unit, but the transmitted data framestorage unit does not need to have the queue structure, and it issufficient that the transmitted data frame storage unit stores at leastsome of the plurality of data frames transmitted to the mobile stationdevices 12 in a manner to allow identification of the timing oftransmission of each of the data frames. For example, it is possible tostore the transmitted data frame in correlation to an identificationnumber of the TDMA frame in which the data frame was transmitted.

The retransmission data frame selecting unit 70 selects, based on areception timing of the retransmission request transmitted from a mobilestation device 12, a data frame to be retransmitted from among theplurality of data frames transmitted to the mobile station device 12.More specifically, based on the timing of reception of the ACKCH fromthe mobile station device 12 acquired by the retransmission requestacquiring unit 64 and the timing difference information (informationindicating the timing difference between the transmission timing of thedata frame and the reception timing of the retransmission request forthe data frame) stored in the timing difference information storage unit66, the retransmission data frame selecting unit 70 identifies thetransmission timing of the data frame corresponding to the ACKCH. Basedon the identified transmission timing, the retransmission data frameselecting unit 70 selects, from among the plurality of data framestransmitted in the past to the mobile station device 12, the data frametransmitted at the identified timing from the transmission-completequeue 68.

As described above, in the present embodiment, because thetransmission-complete queue 68 has a size corresponding to the timingdifference information stored in the timing difference informationstorage unit 66, the ACKCH acquired in each TDMA frame by theretransmission request acquiring unit 64 corresponds to the first dataframe in the transmission-complete queue 68 at the timing of receptionof the ACKCH. Because of this configuration, when the NACK is stored inthe ACKCH, the retransmission data frame selecting unit 70 selects(extracts) the first data frame as the retransmission data frame fromthe transmission-complete queue 68 and adds to the transmission queue60. When, on the other hand, the ACK is stored in the ACKCH, theretransmission data frame selecting unit 70 deletes the first data framefor which no retransmission is required from the transmission-completequeue 68.

Next, an operation of the base station device 10 will be described. FIG.7 is a flowchart showing a data frame transmission (and retransmission)process in the base station device 10.

As shown in FIG. 7, first, in a downlink frame, a data frame including atransmission packet received from an upper device is stored in the databuffer 58 (S100). The data frame is added to the transmission queue 60(S102). Then, the first data frame is extracted from the transmissionqueue 60 and is converted to a transmission signal, and the transmissionsignal is transmitted to the mobile station device 12 (S104). Thetransmitted data frame is added to the transmission-complete queue 68(S106).

Then, in an uplink frame, received data from the mobile station device12 is acquired. The retransmission request acquiring unit 64 acquiresthe ACKCH from the PHY header in the received data and determineswhether the value stored in the ACKCH is ACK or NACK (S108). When thevalue is ACK, the retransmission data frame selecting unit 70 deletesthe first data frame from the transmission-complete queue 68 (S110).Then, it is determined whether or not the data transmission is completed(S112), and, if the transmission is not completed, the processes fromS102 are executed in the next downlink frame.

When, on the other hand, it is determined in S108 that the value storedin the ACKCH is NACK, the retransmission data frame selecting unit 70extracts the first data frame from the transmission-complete queue 68 asa retransmission data frame (S114) and adds to the transmission queue 60(S116). Then, the processes from S104 are executed in the next downlinkframe.

Next, the operation of the mobile station device 12 will be described.FIG. 8 is a flowchart showing an error correction process of thereceived data frame in the mobile station device 12.

First, in a downlink frame, a data frame is received from the basestation device 10 (S200). Then, the maximum ratio combining unit 28maximum-ratio combines the symbol sequence created from the receiveddata frame which is input from the modulation/demodulation unit 26 andthe symbol sequence which is read from the receive buffer 30 based onthe sequence number of the received data frame (S202). The combinedsymbol sequence is stored in the receive buffer 30 in correlation to thesequence number of the received data frame (S204). The combined symbolsequence is converted to a bit sequence in the error correcting unit 32and an error correction is applied (S206).

Next, the error detecting unit 34 determines whether or not there is adata error in the data after error correction which is input from theerror correcting unit 32 (S208) and outputs the detection result to theretransmission request transmission controller 36. When no data error isdetected, the retransmission request transmission timing identifyingunit 40 identifies a transmission timing of the ACK for the receiveddata frame based on the reception timing of the received data frameacquired by the data frame reception timing acquiring unit 38 and thetiming difference information stored in the timing differenceinformation storage unit 42 (S210). The retransmission requesttransmission controller 36 then outputs the ACK to themodulation/demodulation unit 26 such that the ACK is transmitted at atiming identified in S210 (for example, the uplink frame after the nextuplink frame). The ACK which is input to the modulation unit 26 isstored in the ACKCH of the PHY header without the sequence number of thedata frame and is transmitted (S212). Then, the retransmission requesttransmission controller 36 deletes the received data frame correspondingto the ACK from the receive buffer 30 (S214).

When, on the other hand, a data error is detected in S208, theretransmission request transmission timing identifying unit 40identifies the transmission timing of the NACK for the received dataframe based on the reception timing of the received data frame acquiredby the data frame reception timing acquiring unit 38 and the timingdifference information stored in the timing difference informationstorage unit 42 (S216). The retransmission request transmissioncontroller 36 outputs the NACK to the modulation/demodulation unit 26such that the NACK is transmitted at the timing identified in S216 (forexample, the uplink frame following the next uplink frame). The NACKwhich is input to the modulation unit 26 is stored in the ACKCH of thePHY header without the sequence number of the data frame and istransmitted (S218).

According to the above-described embodiment, because the base stationdevice 10 and the mobile station device 12 share the timing difference(time interval) between the transmission (reception) timing of the dataframe and the reception (transmission) timing of the retransmissionrequest for the data frame, even when the sequence number of the dataframe is omitted in the retransmission request, the base station device10 can identify to which data frame the received retransmission requestcorresponds. Because of this configuration, the size of the PHY headersection can be reduced and the size of the PHY body section can beexpanded.

The present invention is not limited to the above-described embodimentand various modified embodiments can be employed. For example, in theabove description, the present invention is applied to a mobilecommunication system which uses SDMA, TDMA, and OFDMA in combination,but the present invention can also be applied to a general communicationsystem having a transmitting device and a receiving device and whichapplies an automatic repeat request method of data frame.

In addition, in the above-described embodiment, a configuration isdescribed in which the mobile station device 12 requests retransmissionof the data frame and the base station device 10 retransmits the dataframe in response to the request, but the present invention can also beapplied to a configuration in which the roles of the mobile stationdevice 12 and the base station device 10 are exchanged or to aconfiguration in which each of the mobile station device 12 and the basestation device 10 has the functions of the retransmission request andthe data frame retransmission.

Second Embodiment

FIG. 9 is an overall configuration diagram of a mobile communicationsystem according to a second embodiment of the present invention. Asshown in FIG. 9, a mobile communication system 1001 includes a basestation device 1010 and a plurality of mobile station devices 1012(here, three mobile station devices).

Each of the mobile station devices 1012 wirelessly communicates with thebase station device 1010, and may be, for example, a portable cellularphone, a personal digital assistant, or a communication card. In thisconfiguration, the mobile station device 1012 transmits and receivesdata to and from the base station device 1010 according to a TDD systemand executes a multiplex communication according to a TDMA system and anOFDMA system. The base station device 1010 includes an adaptive arrayantenna as will be described below, and executes a multiplexcommunication with each of the plurality of mobile station devices 1012at a same time slot and a same carrier frequency according to a spacedivision multiple access (SDMA) using the adaptive array antenna. Withsuch a configuration, a bidirectional communication with the pluralityof mobile station devices 1012 is realized with a very high frequencyusage efficiency.

FIG. 12 is a diagram showing an example of a time slot structure (1 TDMAframe) according to TDMA/TDD and a subchannel structure according toOFDMA. As shown in FIG. 12, each of a downlink (wireless transmissionpath from the base station device 1010 to the mobile station device1012) and an uplink (wireless transmission path from the mobile stationdevice 1012 to the base station device 1010) includes 4 time slots. Eachtime slot includes 28 subchannels, one of which is used as a controlchannel (CCH) and the remaining 27 of which are used as traffic channels(TCH).

The base station device 1010 assigns at least some of a total of 108subchannels (27 subchannels×4 slots) used as the traffic channels toeach of the mobile station devices 1012 in each of the downlink and theuplink. More specifically, as shown in FIG. 12, the base station device1010 assigns one anchor subchannel (ASCH) and assigns one or a pluralityof extra subchannels (ESCH) as necessary, for each mobile station device1012.

The ASCH is a subchannel which is determined when a link is established(at the start of communication) and notified to each of the mobilestation devices 1012 using the CCH, and is primarily used fortransmitting and receiving control information such as MAP informationand ACK information. The MAP information is a bit sequence having alength of 108 bits indicating one or a plurality of ESCH to be used inthe next TDMA frame (next uplink frame and downlink frame) after the MAPinformation is received. More specifically, a bit corresponding to ESCHto be assigned to the mobile station device 1012 in the next TDMA frameis indicated with “1” and bits corresponding to the other subchannels(ASCH, ESCH to be assigned to the other mobile station devices 1012, andidle subchannel) are indicated with “0”. The ACK information stores asequence number of the data frame received in the uplink and ACK(Acknowledge) or NACK (Negative Acknowledge) indicating presence orabsence of an error in the data frame. In particular, when the ACKinformation stores NACK, the ACK information represents a retransmissionrequest of the data frame.

The ESCH, on the other hand, is a subchannel which is determined afterthe link is established and is identified by the MAP informationnotified to the mobile station device 12 using the ASCH, and isprimarily used for transmission and reception of communication data. Asshown in FIG. 12, the ASCH and the ESCH are assigned to the samesubchannel in the downlink slot and the uplink slot having correspondingslot numbers (DL#1 and UP#1, DL#2 and UL#2, . . . ).

FIG. 10 is a functional block diagram of the mobile station device 1012.As shown in FIG. 10, the mobile station device 1012 includes an antenna1020, a wireless communication unit 1022, a signal processor 1024, amodulation/demodulation unit 1026, a data buffer 1028, an external I/Funit 1032, a data input unit 1034, a data frame retransmissioncontroller 1036, and a storage unit 1046.

The wireless communication unit 1022 includes a low noise amplifier, adown-converter, and an up-converter. The wireless communication unit1022 down-converts a wireless signal from the base station device 1010received by the antenna 1020 and outputs to the signal processor 1024.The wireless communication unit 1022 also up-converts a transmissionsignal which is input from the signal processor 1024 into a wirelesssignal, amplifies the wireless signal to a transmission power level, andtransmits from the antenna 1020.

The signal processor 1024 applies processes such as symbolsynchronization and removal of a guard interval (GI) signal on thesignal which is input from the wireless communication unit 1022, toacquire a baseband OFDM signal, and outputs to themodulation/demodulation unit 1026. The signal processor 1024 also adds aguard interval signal to a baseband OFDM signal which is input from themodulation/demodulation unit 1026 and outputs to the wirelesscommunication unit 1022.

The modulation/demodulation unit 1026 includes an A/D converter, an FFTunit, a channel estimation unit, and a de-mapping unit. Themodulation/demodulation unit 1026 OFDM-demodulates the baseband OFDMsignal which is input from the signal processor 1024 and outputs theacquired received data frame to the data buffer 1028. More specifically,the modulation/demodulation unit 1026 applies an A/D conversion on thebaseband OFDM signal and then applies an FFT in the FFT unit, to acquiresubcarrier components of the OFDM symbol. Then, after themodulation/demodulation unit 1026 applies a predetermined channelestimation process or the like, the modulation/demodulation unit 1026connects the subcarrier components corresponding to a plurality ofsubchannels (one ASCH and one or a plurality of ESCH) assigned by thebase station device 1010 referring to the assignment status ofsubchannels stored in a channel information storage unit 1048, to createa symbol sequence. The modulation/demodulation unit 1026 outputs thereceived data frame acquired by decoding the symbol sequence to the databuffer 1028.

The modulation/demodulation unit 1026 also includes a symbol mappingunit, an IFFT unit, and a D/A converter. The modulation/demodulationunit 1026 OFDM-modulates a transmission data frame which is input fromthe data buffer 1028 (transmission queue 1030) and outputs the acquiredbaseband OFDM signal to the signal processor 1024. More specifically,the modulation/demodulation unit 1026 divides the transmission dataframe referring to the assignment status of subchannels stored in thechannel information storage unit 1048, and creates transmission datacorresponding to each of the plurality of subchannels (one ASCH and oneor a plurality of ESCH) assigned by the base station device 1010. Then,the modulation/demodulation unit 1026 converts the created transmissiondata of each of the subchannels into a symbol sequence through a symbolmapping, and distributes the symbol sequence over the subcarriers of thesubchannel. The modulation/demodulation unit 1026 then applies an IFFTin the IFFT unit and outputs the baseband OFDM signal acquired through aD/A conversion to the signal processor 1024.

The data buffer 1028 includes the transmission queue 1030. The databuffer 1028 temporarily stores the received data frames from the basestation device 1010 which are input from the modulation/demodulationunit 1026 and sequentially outputs received data which is acquired byconnecting the received data frames to an upper device (not shown)through the predetermined external I/F unit 1032. The data buffer 1028also temporarily stores transmission data frames to each of the mobilestation devices 1012 which are input from the upper device through theexternal I/F unit 1032 and data which is input from the data input unit1034 such as a numerical pad, creates a transmission data frame based onthese transmission data, and sequentially outputs to themodulation/demodulation unit 1026 through the transmission queue 1030.

The transmission queue 1030 holds the transmission data frame in a liststructure of a First In First Out (FIFO) method. The transmission dataframe or the retransmission data frame which is input from the dataframe retransmission controller 1036 is added to the transmission queue1030 in each TDMA frame. The first data frame in the transmission queue1030 is extracted in each TDMA frame and is output to themodulation/demodulation unit 1026.

The storage unit 1046 includes a memory, and also includes the channelinformation storage unit 1048 and a timing difference informationstorage unit 1050.

The channel information storage unit 1048 stores the subchannels (oneASCH and one or a plurality of ESCH) assigned by the base station device1010. Because the ASCH is the subchannel for transmitting the ACKinformation, the slot position of the ASCH represents the receptiontiming (reception slot) of the ACK information.

The timing difference information storage unit 1050 stores, incorrelation to information indicating a reception timing of a NACK,timing difference information indicating a timing difference whichsatisfies a condition related to a reference required time. Here, thereference required time is the minimum time which is required for aprocess from the reception of the NACK to the retransmission of the dataframe (hereinafter referred to as data frame retransmission process),and is set, for example, with reference to the mobile station device1012 having the slowest process executing speed (the lowest processingcapability). The timing difference which satisfies a condition relatedto the reference required time is a timing difference between thereception timing of the NACK and the retransmission timing of the dataframe corresponding to the NACK, and is a timing difference which isgreater than or equal to the reference required time and which is asclose to the reference required time as possible. The reception timingof the NACK may be identified by the reception slot of the NACK, and theretransmission timing of the data frame may be identified by thetransmission slot of the retransmission data frame or the transmissionframe including the transmission slot.

FIG. 11 is a diagram showing an example of the timing differenceinformation storage unit 1050. As shown in FIG. 11, the timingdifference information storage unit 1050 stores timing differenceinformation (timing 1, timing 2) in correlation to the slot position ofthe ASCH (subchannel for transmitting the ACK information). This showsthe correspondence relationship between the slot position of the ASCHindicating the reception slot of the NACK and the transmission frameindicating the timing of the retransmission of the data framecorresponding to the NACK, and the transmission frame is set such thatthe reference required time required for the data frame retransmissionprocess in the mobile station device 1012 is secured and is minimized.In other words, the information shown in the timing differenceinformation storage unit 1050 shown in FIG. 11 indicates, for each slotposition of ASCH indicating the reception slot of the NACK, an optimumtransmission frame which secures the reference required time andminimizes the data frame retransmission process time. Because of this,for example, when the NACK is received in the “first slot” (when theslot position of ASCH is the “first slot”), if the data frame isretransmitted in the next frame of the reception slot (timing 1), thedata frame retransmission process time is minimized.

The data frame retransmission controller 1036 includes a retransmissionrequest acquiring unit 1038, a data frame retransmission timingdetermining unit 1040, a transmission-complete buffer 1042, and aretransmission data frame selecting unit 1044. The data frameretransmission controller 1036 controls, in response to a retransmissionrequest transmitted from the base station device 1010, retransmission ofthe data frame corresponding to the retransmission request.

The retransmission request acquiring unit 1038 acquires the ACKinformation in each TDMA frame from the received data which is outputfrom the data buffer 1028 and acquires the reception timing (receptionslot) of the ACK information.

The data frame retransmission timing determining unit 1040 determines,based on the reception timing of the NACK, the retransmission timing(transmission slot or transmission frame) of the data framecorresponding to the NACK so that the timing difference between thereception timing of the NACK and the retransmission timing of the dataframe corresponding to the NACK is close to the reference required timerequired for the data frame retransmission process.

FIG. 13 is a diagram for explaining a retransmission timing of the dataframe identified by the data frame retransmission timing determiningunit 1040. As shown in FIG. 13( a), when the slot position of the ASCHindicating the reception slot of the NACK is the first slot, the dataframe retransmission timing determining unit 1040 determines the nexttransmission frame of the NACK reception slot as the data frameretransmission timing. This determination is based on design andexperimental results that all mobile station devices 1012 can completethe retransmission process of the data frame within time period ofapproximately 3 slots from the NACK reception slot to the nexttransmission frame. In this case, the data frame retransmission processtime can be shortened by at least 1 TDMA frame compared to the relatedart. When, on the other hand, the slot position of the ASCH (NACKreception slot) is the fourth slot as shown in FIG. 13( b), the dataframe retransmission timing determining unit 1040 determines atransmission frame following the next transmission frame of the NACKreception slot as the data frame retransmission timing. Thisdetermination is based on design and experimental results that it isdifficult for all mobile station devices 1012 to complete the data frameretransmission process within a time period from the NACK reception slotto the next transmission frame (about 0 slot).

The data frame retransmission timing determining unit 1040 may read thetiming difference information from the timing difference informationstorage unit 1050 in correlation to the slot position of the ASCHindicating the reception slot of the NACK and determine a retransmissiontiming (transmission frame) of the data frame corresponding to the NACKbased on the reception slot of the NACK and the read timing differenceinformation.

The transmission-complete buffer 1042 temporarily stores at least someof the plurality of data frames transmitted to the base station device1010 in correlation to the sequence number of each of the data frames.The first data frame in the transmission queue 1030 is transmitted ineach TDMA frame, and, with the transmission, the data frame is extractedfrom the transmission queue 1030 and stored in the transmission-completebuffer 1042.

The retransmission data frame selecting unit 1044 selects, when the NACKis stored in the ACK information acquired by the retransmission requestacquiring unit 1038, a data frame to be retransmitted from thetransmission-complete buffer 1042 based on the sequence number of thedata frame stored in the ACK information, and adds the data frame to thetransmission queue 1030. On the other hand, when the ACK is stored inthe ACK information, the retransmission data frame selecting unit 1044deletes the data frame corresponding to the sequence number of the dataframe stored in the ACK information from the transmission-completebuffer 1042.

An operation of the mobile station device 1012 will now be described.

FIG. 14 is a flowchart showing a process of acquiring the timingdifference information at the start of the communication. As shown inFIG. 14, when the communication is started, the channel informationstorage unit 1048 stores one ASCH and one or a plurality of ESCHassigned by the base station device 1010. Then, the data frameretransmission timing determining unit 1040 acquires the slot positionof the ASCH from the channel information storage unit 1048 (S1100). Inaddition, the data frame retransmission timing determining unit 1040acquires the timing difference information from the timing differenceinformation storage unit 1050 in correlation to the acquired slotposition of the ASCH (S1102).

FIG. 15 is a flowchart showing the data frame transmission (andretransmission) in the mobile station device 1012. As shown in FIG. 15,first, in an uplink frame, a data frame including a transmission packetreceived from an upper device is stored in the data buffer 1028 (S1200).Then, the data frame is added to the transmission queue 1030 (S1202).Next, the first data frame is extracted from the transmission queue1030, the data frame is converted to a transmission signal, and thetransmission signal is transmitted to the base station device 1010(S1204). The transmitted data frame is stored in thetransmission-complete buffer 1042 in correlation to its sequence number(S1206).

Then, in a downlink frame, the received data from the base stationdevice 1010 is acquired. The retransmission request acquiring unit 1038acquires the ACK information from the received data and determineswhether the value stored in the ACK information is ACK or NACK (S1208).When the value is ACK, the retransmission data frame selecting unit 1044deletes, based on the sequence number of the data frame stored in theACK information, the corresponding data frame from thetransmission-complete buffer 1042 (S1210). It is then determined whetheror not the data transmission is completed (S1212), and, if thetransmission is not completed, the processes from S1202 are executed inthe next uplink frame.

When, on the other hand, the value stored in the ACK information is NACKin S1208, the data frame retransmission timing determining unit 1040determines the transmission frame of the data frame corresponding to theNACK based on the reception slot of the NACK acquired by theretransmission request acquiring unit 1038 and the timing differenceinformation acquired in S1102 (S1214). Then, the retransmission dataframe selecting unit 1044 selects a data frame to be retransmitted fromthe transmission-complete buffer 1042 based on the sequence number ofthe data frame stored in the ACK information (S1216), and adds the dataframe to the transmission queue 1030 so that the data frame istransmitted in the transmission frame determined in S1214 (S1218). Then,in the next uplink frame, the processes from S1204 are executed.

According to the above-described embodiment, the retransmission timing(transmission frame) of the data frame corresponding to the NACK isdetermined based on the reception timing (reception slot) of the NACK sothat the time from the reception of the NACK to the retransmission ofthe data frame corresponding to the NACK is close to the referencerequired time required for the data frame retransmission process.Because of this configuration, it is possible to preferably shorten thetime from the reception of the NACK to the retransmission of the dataframe.

The present invention is not limited to the above-described embodimentand various modified embodiments may be employed. For example, in theabove description, the present invention is applied to the mobilestation device in a mobile communication system which uses SDMA,TDMA/TDD, and OFDMA in combination, but the present invention can beapplied to a general communication device which employs a TDMA/TDD andan automatic repeat request method of data frame.

In addition, in the above-described embodiment, a configuration isdescribed in which the mobile station device 1012 retransmits a dataframe in response to a data frame retransmission request from the basestation device 1010, but the present invention can be applied to aconfiguration in which the roles of the mobile station device 1012 andthe base station device 1010 are exchanged or to a configuration inwhich each of the mobile station device 1012 and the base station device1010 has the functions of the retransmission request and the data frameretransmission.

Third Embodiment

FIG. 16 is an overall configuration diagram of a mobile communicationsystem according to a third embodiment of the present invention. Asshown in FIG. 16, a mobile communication system 2001 includes a basestation device 2010 and a plurality of mobile station devices 2012(here, three mobile station devices).

Each of the mobile station devices 2012 wirelessly communicates with thebase station device 2010, and may be, for example, a portable cellularphone, a personal digital assistant, or a communication card. In thisconfiguration, the mobile station device 2012 transmits and receivesdata to and from the base station device 2010 according to a TDD systemand executes a multiplex communication according to a TDMA system and anOFDMA system. The base station device 2010 includes an adaptive arrayantenna as will be described below, and executes a multiplexcommunication with each of the plurality of mobile station devices 2012at a same time slot and a same carrier frequency according to a spacedivision multiple access system (SDMA) using the adaptive array antenna.With such a configuration, a bidirectional communication with theplurality of mobile station devices 2012 is achieved with a very highfrequency usage efficiency.

FIG. 19 is a diagram showing an example of a time slot structure (1 TDMAframe) according to TDMA/TDD and a subchannel structure according toOFDMA. As shown in FIG. 19, each of a downlink (wireless transmissionpath from the base station device 2010 to the mobile station device2012) and an uplink (wireless transmission path from the mobile stationdevice 2012 to the base station device 2010) includes 4 time slots. Eachtime slot includes 28 subchannels, one of which is used as a controlchannel (CCH) and the remaining 27 of which are used as traffic channels(TCH).

The base station device 2010 assigns at least some of a total of 108subchannels (27 subchannels×4 slots) used as the traffic channels toeach of the mobile station devices 2012 in each of the downlink and theuplink. More specifically, as shown in FIG. 19, the base station device2010 assigns one anchor subchannel (ASCH) and assigns one or a pluralityof extra subchannels (ESCH) as necessary, for each mobile station device2012.

The ASCH is a subchannel which is determined when a link is established(at the start of communication) and notified to each of the mobilestation devices 2012 using the CCH, and is primarily used fortransmission and reception of control information such as MAPinformation and ACK information. The MAP information is a bit sequencehaving a length of 108 bits indicating one or a plurality of ESCH to beused in the next TDMA frame (next uplink frame and downlink frame) afterthe MAP information is received. More specifically, a bit correspondingto ESCH to be assigned to the mobile station device 2012 in the nextTDMA frame is indicated with “1”, and bits corresponding to the othersubchannels (ASCH, ESCH to be assigned to other mobile station devices2012, and idle subchannel) are indicated with “0”. The ACK informationstores a sequence number of the data frame received in the uplink andACK (Acknowledge) or NACK (Negative Acknowledge) indicating presence orabsence of an error in the data frame. In particular, when the ACKinformation stores NACK, the ACK information represents a retransmissionrequest of the data frame.

The ESCH, on the other hand, is a subchannel which is determined afterthe link is established and is identified by the MAP informationnotified to the mobile station device 12 using the ASCH, and isprimarily used for transmission and reception of communication data. Asshown in FIG. 19, the ASCH and the ESCH are assigned in the samesubchannels in the downlink slot and uplink slot having correspondingslot numbers (DL#1 and UL#1, DK#2 and UL#2, . . . ).

FIG. 17 is a functional block diagram of the mobile station device 2012.As shown in FIG. 17, the mobile station device 2012 includes an antenna2020, a wireless communication unit 2022, a signal processor 2024, amodulation/demodulation unit 2026, a data buffer 2028, an external I/Funit 2032, a data input unit 2034, a data frame retransmissioncontroller 2036, and a storage unit 2046.

The wireless communication unit 2022 includes a low noise amplifier, adown-converter, and an up-converter. The wireless communication unit2022 down-converts a wireless signal from the base station device 2010received by the antenna 2020 and outputs to the signal processor 2024.The wireless communication unit 2022 also up-converts a transmissionsignal which is input from the signal processor 2024 into a wirelesssignal, amplifies the wireless signal to a transmission power level, andtransmits from the antenna 2020.

The signal processor 2024 applies processes such as symbolsynchronization and removal of a guard interval (GI) signal on thesignal which is input from the wireless communication unit 2022, toacquire a baseband OFDM signal, and outputs to themodulation/demodulation unit 2026. In addition, the signal processor2024 adds a guard interval signal to a baseband OFDM signal which isinput from the modulation/demodulation unit 2026 and outputs to thewireless communication unit 2022.

The modulation/demodulation unit 2026 includes an A/D converter, an FFTunit, a channel estimation unit, and a de-mapping unit. Themodulation/demodulation unit 2026 OFDM-demodulates the baseband OFDMsignal which is input from the signal processor 2024 and outputs theacquired received data frame to the data buffer 2028. More specifically,after the modulation/demodulation unit 2026 A/D-converts the basebandOFDM signal, the modulation/demodulation unit 2026 applies an FFT in theFFT unit, to acquire the subcarrier components of the OFDM symbol. Then,after the modulation/demodulation unit 2026 applies a predeterminedchannel estimation process or the like, the modulation/demodulation unit2026 connects the subcarrier components corresponding to a plurality ofsubchannels (one ASCH and one or a plurality of ESCH) assigned by thebase station device 2010 referring to the assignment status ofsubchannels stored in a channel information storage unit 2050, to createa symbol sequence. The modulation/demodulation unit 2026 outputs thereceived data frame acquired by decoding the symbol sequence to the databuffer 2028.

The modulation/demodulation unit 2026 also includes a symbol mappingunit, an IFFT unit, and a D/A converter. The modulation/demodulationunit 2026 OFDM-modulates a transmission data frame which is input fromthe data buffer 2028 (transmission queue 2030) and outputs the acquiredbaseband OFDM signal to the signal processor 2024. More specifically,the modulation/demodulation unit 2026 divides the transmission dataframe referring to the assignment status of subchannels stored in thechannel information storage unit 2050, and creates transmission datacorresponding to each of the plurality of subchannels (one ASCH and oneor a plurality of ESCH) assigned by the base station device 2010. Then,the modulation/demodulation unit 2026 converts the created transmissiondata of each of the subchannels into a symbol sequence through a symbolmapping, and distributes the symbol sequence over the subcarriers of thesubchannel. The modulation/demodulation unit 2026 applies an IFFT in theIFFT unit, and outputs the baseband OFDM signal acquired through a D/Aconversion to the signal processor 2024.

The data buffer 2028 includes the transmission queue 2030. The databuffer 2028 temporarily stores the received data frames from the basestation device 2010 which are input from the modulation/demodulationunit 2026 and sequentially outputs the received data acquired byconnecting the received data frames to an upper device (not shown)through the predetermined external I/F unit 2032. In addition, the databuffer 2028 temporarily stores transmission data frames to each of themobile station devices 2012 which are input from the upper devicethrough the external I/F unit 2032 and the data which is input from thedata input unit 2034 such as a numerical pad, creates a transmissiondata frame based on these transmission data, and sequentially outputs tothe modulation/demodulation unit 2026 through the transmission queue2030.

The transmission queue 2030 holds the transmission data frame in a liststructure of a First In First Out (FIFO) method. The transmission dataframe or the retransmission data frame which is input from the dataframe retransmission controller 2036 is added to the transmission queue2030 in each TDMA frame. The first data frame in the transmission queue2030 is extracted in each TDMA frame and output to themodulation/demodulation unit 2026.

The storage unit 2046 includes a memory, and also includes a processingcapability storage unit 2048, the channel information storage unit 2050,and a timing difference information storage unit 2052.

The processing capability storage unit 2048 stores informationindicating the processing capability of the mobile station device 2012(for example, level 1). In general, a device with a higher processingcapability can complete each process in shorter time.

The channel information storage unit 2050 stores the subchannels (oneASCH and one or a plurality of ESCH) assigned by the base station device2010. Because the ASCH is a subchannel for transmitting the ACKinformation, the slot position of the ASCH indicates the receptiontiming (reception slot) of the ACK information.

The timing difference information storage unit 2052 stores, incorrelation to information indicating the processing capability of themobile station device 2012 and information indicating a reception timingof a NACK, timing difference information indicating a timing differencewhich satisfies a condition related to a reference required time. Here,the reference required time is the minimum time required for the processfrom the reception of the NACK to the retransmission of the data frame(hereinafter referred to as data frame retransmission process) andvaries according to the process executing speed of the mobile stationdevice 2012. In other words, the reference required time is shorter fora mobile station device 2012 having a higher processing capability andis longer for a mobile station device 2012 having a lower processingcapability. The timing difference which satisfies a condition related tothe reference required time is a timing difference between the receptiontiming of the NACK and the retransmission timing of the data framecorresponding to the NACK, and is a timing difference which is greaterthan or equal to the reference required time and which is as close tothe reference required time as possible. The reception timing of theNACK may be identified by the reception slot of the NACK, and theretransmission timing of the data frame may be identified by thetransmission slot of the retransmission data frame or the transmissionframe including the transmission slot.

FIG. 18 is a diagram showing an example of the timing differenceinformation storage unit 2052. As shown in FIG. 18, the timingdifference information storage unit 2052 stores timing differenceinformation (timing 1, timing 2) in correlation to informationindicating the processing capability of the mobile station device 2012(level 0, level 1, . . . ) and the slot position of the ASCH (subchannelfor transmitting the ACK information). This indicates a correspondencerelationship between the slot position of the ASCH indicating thereception slot of the NACK and the transmission frame indicating thetiming of the retransmission of the data frame corresponding to theNACK, and the transmission frame is set so that the reference requiredtime required for the data frame retransmission process in the mobilestation device 2012 is secured and minimized. Because the referencerequired time varies according to the processing capability indicatingthe process executing speed of the mobile station device 2012 asdescribed above, FIG. 18 shows a plurality of the correspondencerelationships (in this configuration, five correspondence relationships)for each processing capability of the mobile station device 2012. Inother words, the information indicated in the timing differenceinformation storage unit 2052 shown in FIG. 18 indicates, for each slotposition of ASCH indicating the reception slot of the NACK, an optimumtransmission frame which secures the reference required timecorresponding to the processing capability of the mobile station device2012 and minimizes the data frame retransmission process time. Becauseof this, for example, when the processing capability of the mobilestation device 2012 is “level 1” and the NACK is received in the “thirdslot” (when the slot position of the ASCH is the “third slot”), the dataframe retransmission process time is shortened by the maximum amount ifthe data frame is retransmitted in the next frame of the reception slot(timing 1).

The data frame retransmission controller 2036 includes a retransmissionrequest acquiring unit 2038, a data frame retransmission timingdetermining unit 2040, a transmission-complete buffer 2042, and aretransmission data frame selecting unit 2044. The data frameretransmission controller 2036 controls, in response to a retransmissionrequest transmitted from the base station device 2010, retransmission ofthe data frame corresponding to the retransmission request.

The retransmission request acquiring unit 2038 acquires the ACKinformation in each TDMA frame from the received data which is outputfrom the data buffer 2028 and acquires the reception timing (receptionslot) of the ACK information.

The data frame retransmission timing determining unit 2040 determinesthe retransmission timing (transmission slot or transmission frame) ofthe data frame corresponding to the NACK based on the processingcapability of the mobile station device 2012 so that the timingdifference between the reception timing of the NACK and theretransmission timing of the data frame corresponding to the NACK isclose to the reference required time required for the data frameretransmission process.

FIG. 20 is a diagram for explaining a retransmission timing of the dataframe identified by the data frame retransmission timing determiningunit 2040. FIG. 20 shows a case where the slot position of the ASCHindicating the reception slot of the NACK is the first slot. As shown inFIG. 20( a), when the processing capability (process executing speed) ofthe mobile station device 2012 is high, the data frame retransmissiontiming determining unit 2040 determines the next transmission frame ofthe NACK reception slot as the data frame retransmission timing. Thisdetermination is based on design and experimental results that a mobilestation device 2012 having a high processing capability can complete theretransmission process of the data frame within time period ofapproximately 3 slots from the NACK reception slot to the nexttransmission frame. In this case, the data frame retransmission processtime can be shortened by at least 1 TDMA frame compared to the relatedart. When, on the other hand, the processing capability (processexecuting speed) of the mobile station device 2012 is low as shown inFIG. 20( b), the data frame retransmission timing determining unit 2040determines a transmission frame following the next transmission frame ofthe NACK reception slot as the data frame retransmission timing. Thisdetermination is based on design and experimental results that, with themobile station device 2012 having a low processing capability, althoughit is difficult to complete the data frame retransmission process in thetime from the NACK reception slot to the next transmission frame(approximately 0 slot), the data frame retransmission process can becompleted if there is time until the transmission frame following thenext transmission frame. The data frame retransmission timingdetermining unit 2040 may determine the retransmission frame of the dataframe further based on the reception timing (reception slot) of theNACK.

Alternatively, the data frame retransmission timing determining unit2040 may read the timing difference information from the timingdifference information storage unit 2052 in correlation to theprocessing capability of the mobile station device 2012 and the slotposition of the ASCH indicating the reception slot of the NACK anddetermine the retransmission timing (transmission frame) of the dataframe corresponding to the NACK based on the reception slot of the NACKand the read timing difference information.

The transmission-complete buffer 2042 temporarily stores at least someof the plurality of data frames transmitted to the base station device2010, in correlation to the sequence number of each of the data frames.The first data frame in the transmission queue 2030 is transmitted ineach TDMA frame, and, with the transmission, the data frame is extractedfrom the transmission queue 2030 and stored in the transmission-completebuffer 2042.

The retransmission data frame selecting unit 2044 selects, when the NACKis stored in the ACK information acquired by the retransmission requestacquiring unit 2038, a data frame to be retransmitted from thetransmission-complete buffer 2042 based on the sequence number of thedata frame stored in the ACK information, and adds to the transmissionqueue 2030. When the ACK is stored in the ACK information, theretransmission data frame selecting unit 2044 deletes the data framecorresponding to the sequence number of the data frame stored in the ACKinformation from the transmission-complete buffer 2042.

An operation of the mobile station device 2012 will now be described.

FIG. 21 is a flowchart showing a process for acquiring the timingdifference information at the start of the communication. As shown inFIG. 21, when the communication is started, the channel informationstorage unit 2050 stores one ASCH and one or a plurality of ESCHassigned by the base station device 2010. Then, the data frameretransmission timing determining unit 2040 acquires the processingcapability of the mobile station device 2012 from the processingcapability storage unit 2048 (S2100). The data frame retransmissiontiming determining unit 2040 also acquires the slot position of the ASCHfrom the channel information storage unit 2050 (S2102). The data frameretransmission timing determining unit 2040 acquires the timingdifference information from the timing difference information storageunit 2052 in correlation to the acquired processing capability of themobile station device 2012 and the slot position of the ASCH (S2104).

FIG. 22 is a flowchart showing a data frame transmission (andretransmission) in the mobile station device 2012. As shown in FIG. 22,first, in an uplink frame, a data frame including a transmission packetreceived from an upper device is stored in the data buffer 2028 (S2200).Then, the data frame is added to the transmission queue 2030 (S2202).Next, the first data frame is extracted from the transmission queue2030, converted to a transmission signal, and transmitted to the basestation device 2010 (S2204). The transmitted data frame is stored in thetransmission-complete buffer 2042 in correlation to its sequence number(S2206).

Next, in a downlink frame, the received data from the base stationdevice 2010 is acquired. The retransmission request acquiring unit 2038acquires the ACK information from the received data and determineswhether the value stored in the ACK information is ACK or NACK (S2208).When the value is ACK, the retransmission data frame selecting unit 2044deletes, based on the sequence number of the data frame stored in theACK information, the corresponding data frame from thetransmission-complete buffer 2042 (S2210). It is then determined whetheror not the data transmission is completed (S2212), and, if thetransmission is not completed, the processes from S2202 are executed inthe next uplink frame.

When, on the other hand, the value stored in the ACK information is NACKin S2208, the data frame retransmission timing determining unit 2040determines the transmission frame of the data frame corresponding to theNACK based on the reception slot of the NACK acquired by theretransmission request acquiring unit 2038 and the timing differenceinformation acquired in S2104 (S2214). Then, the retransmission dataframe selecting unit 2044 selects a data frame to be retransmitted fromthe transmission-complete buffer 2042 based on the sequence number ofthe data frame stored in the ACK information (S2216), and adds to thetransmission queue 2030 so that the data frame is transmitted in thetransmission frame determined in S2214 (S2218). At the next uplinkframe, the processes from S2204 are executed.

According to the above-described embodiment, the retransmission timing(transmission frame) of the data frame corresponding to the NACK isdetermined in consideration of the processing capability of the mobilestation device 2012 so that the time from the reception of the NACK tothe retransmission of the data frame corresponding to the NACK is closeto the reference required time required for the retransmission processof the data frame. Because of this configuration, it is possible topreferably shorten the time from the reception of the NACK to theretransmission of the data frame.

The present invention is not limited to the above-described embodiment,and various modified embodiments may be employed. For example, in theabove description, the present invention is applied to the mobilestation device in a mobile communication system which uses SDMA,TDMA/TDD, and OFDMA in combination, but the present invention can beapplied to a general communication device which employs a TDMA/TDD andan automatic repeat request method of data frame.

1. A communication system having a transmitting device and a receivingdevice which employ an automatic repeat request method of a data frame,wherein the receiving device comprises retransmission requesttransmission timing identifying means for identifying, based on a timingof reception of a data frame transmitted from the transmitting device, atiming of transmission of a retransmission request of the data frame tothe transmitting device, the transmitting device comprisesretransmission data frame selecting means for selecting, based on atiming of reception of the retransmission request transmitted from thereceiving device, a data frame to be retransmitted from among aplurality of data frames transmitted to the receiving device, andretransmits the data frame selected by the retransmission data frameselecting means to the receiving device.
 2. The communication systemaccording to claim 1, wherein the transmitting device further comprisestransmitted data frame storage means for storing at least some of theplurality of data frames transmitted to the receiving device in a mannerto allow identification of a timing of transmission of each of the dataframes, and the retransmission data frame selecting means identifies atiming of transmission of the data frame to be retransmitted based onthe timing of reception of the retransmission request and selects thedata frame to be retransmitted from the transmitted data frame storagemeans based on the identified timing.
 3. The communication systemaccording to claim 1, wherein the communication system further employs atime division multiplex communication system, and the timing isidentified by a time slot or a time frame according to time divisionmultiplexing.
 4. A receiving device which receives a data frametransmitted from a transmitting device and which transmits, upondetection of an error in the received data frame, a retransmissionrequest of the data frame to the transmitting device, the receivingdevice comprising: retransmission request transmission timingidentifying means for identifying, based on a timing of reception of thedata frame, a timing of transmission of the retransmission request ofthe data frame.
 5. A transmitting device which transmits a data frame toa receiving device and which retransmits, in response to aretransmission request from the receiving device, a data framecorresponding to the retransmission request, the transmitting devicecomprising: retransmission data frame selecting means for selecting,based on a timing of reception of the retransmission request, a dataframe to be retransmitted from among a plurality of data framestransmitted to the receiving device, and retransmits a data frameselected by the retransmission data frame selecting means to thereceiving device.
 6. A data frame retransmission control method in acommunication system having a transmitting device and a receivingdevice, the data frame retransmission control method comprising: aretransmission request transmission timing identifying step ofidentifying, based on a timing at which the receiving device receives adata frame transmitted from the transmitting device, a timing oftransmission of a retransmission request of the data frame to thetransmitting device, and a retransmission data frame selecting step ofselecting, based on a timing at which the transmitting device receivesthe retransmission request, a data frame to be retransmitted from amonga plurality of data frames transmitted to the receiving device.
 7. Acommunication device which communicates with another communicationdevice according to a time division duplex system and which retransmits,in response to a retransmission request transmitted from the othercommunication device, a data frame corresponding to the retransmissionrequest to the other communication device, the communication devicecomprising: data frame retransmission timing determining means fordetermining a retransmission timing of the data frame based on areception timing of the retransmission request so that a timingdifference between the reception timing of the retransmission requestand the retransmission timing of the data frame corresponding to theretransmission request is close to a reference required time requiredfrom reception of a retransmission request to retransmission of a dataframe.
 8. The communication device according to claim 7, furthercomprising: timing difference information storage means for storing, incorrelation to information indicating a reception timing of aretransmission request, timing difference information indicating atiming difference which satisfies a condition related to the referencerequired time, wherein the data frame retransmission timing determiningmeans reads timing difference information from the timing differenceinformation storage means in correlation to the reception timing of theretransmission request and determines the retransmission timing of thedata frame based on the reception timing of the retransmission requestand the read timing difference information.
 9. A communication devicewhich communicates with another communication device according to a timedivision duplex system and which retransmits, in response to aretransmission request transmitted from the other communication device,a data frame corresponding to the retransmission request to the othercommunication device, the communication device comprising: data frameretransmission timing determining means for determining a retransmissiontiming of the data frame based on a processing capability of thecommunication device so that a timing difference between a receptiontiming of the retransmission request and the retransmission timing ofthe data frame corresponding to the retransmission request is close to areference required time required from reception of a retransmissionrequest to retransmission of a data frame.
 10. The communication deviceaccording to claim 9, wherein the data frame retransmission timingdetermining means determines the retransmission timing of the data framefurther based on the reception timing of the retransmission request. 11.The communication device according to claim 10, further comprising:timing difference information storage means for storing, in correlationto information indicating a processing capability of a communicationdevice and information indicating a reception timing of a retransmissionrequest, timing difference information indicating a timing differencewhich satisfies a condition related to the reference required time,wherein the data frame retransmission timing determining means reads thetiming difference information from the timing difference informationstorage means in correlation to the processing capability of thecommunication device and the reception timing of the retransmissionrequest and determines the retransmission timing based on the receptiontiming of the retransmission request and the read timing differenceinformation.
 12. The communication device according to claim 7, whereinthe reception timing is identified by a reception slot, and theretransmission timing is identified by a transmission slot or atransmission frame including the transmission slot.
 13. A data frameretransmission method in which a data frame is retransmitted in responseto a retransmission request in a communication according to a timedivision duplex system, the data frame retransmission method comprising:a step of determining a retransmission timing of the data frame based ona reception timing of the retransmission request so that a timingdifference between the reception timing of the retransmission requestand the retransmission timing of the data frame corresponding to theretransmission request is close to a reference required time requiredfrom reception of a retransmission request to retransmission of a dataframe.
 14. A data frame retransmission method in which a data frame isretransmitted in response to a retransmission request in a communicationaccording to a time division duplex system, the data frameretransmission method comprising: a step of determining a retransmissiontiming of the data frame based on a processing capability of thecommunication device so that a timing difference between a receptiontiming of the retransmission request and the retransmission timing ofthe data frame corresponding to the retransmission request is close to areference required time required from reception of a retransmissionrequest to retransmission of a data frame.
 15. The communication systemaccording to claim 2, wherein the communication system further employs atime division multiplex communication system, and the timing isidentified by a time slot or a time frame according to time divisionmultiplexing.
 16. The communication device according to claim 8, whereinthe reception timing is identified by a reception slot, and theretransmission timing is identified by a transmission slot or atransmission frame including the transmission slot.
 17. Thecommunication device according to claim 9, wherein the reception timingis identified by a reception slot, and the retransmission timing isidentified by a transmission slot or a transmission frame including thetransmission slot.
 18. The communication device according to claim 10,wherein the reception timing is identified by a reception slot, and theretransmission timing is identified by a transmission slot or atransmission frame including the transmission slot.
 19. Thecommunication device according to claim 11, wherein the reception timingis identified by a reception slot, and the retransmission timing isidentified by a transmission slot or a transmission frame including thetransmission slot.